This invention relates generally to improvements in closed circuit television systems of the type designed for magnifying or enlarging images such as written text and the like for reading or viewing by persons afflicted with vision impairment. More specifically, this invention relates to such television systems having improved and relatively economical means for rapidly and automatically adjusting image focus to a substantially optimized image quality or resolution.
Closed circuit television systems are generally well known in the art to include a video monitor for displaying images generated electronically by an associated video camera. The video camera includes means for generating a video signal comprising an electronic representation of the desired image or images, and this video signal is coupled to the monitor for appropriate demodulation and display. An adjustable lens on the camera is provided to alter the camera focus setting according to the image range such that the image is displayed on the monitor in relatively sharp focus.
While closed circuit television systems have been used in many different environments, one important system application comprises magnification or enlargement of images such as written text and the like to permit reading and viewing by persons with restricted vision. More specifically, a significant number of individuals are afflicted with impaired vision capacity attributable to a variety of causes, wherein such individuals are generally unable to read or write in a normal manner utilizing written images of a standard size. However, many of these individuals possess sufficient vision capacity to read and/or view such images in an enlarged state. To this end, closed circuit television systems have been developed to include a video camera with a relatively short focal length lens for producing electronic signals representing written material and the like for display in enlarged form on the screen of a video monitor. Such systems commonly include a relatively compact support frame for the camera and monitor, together with a support platen for receiving the written material or the like to be viewed. A rotatable focus control knob is normally provided for adjusting the camera lens to obtain relatively sharply focused images displayed by the monitor. Exemplary of such television systems for use by partially sighted persons are the systems marketed by VTEK of Santa Monica, Calif., under the name Voyager.
Although closed circuit television systems with image magnification constitute a valuable tool for persons with impaired vision, focus adjustment of such systems can be difficult or even impossible. That is, many individuals have inadequate visual acuity to discern easily between good and poor focus settings. Moreover, some individuals have insufficient manual dexterity for adjusting a manual focus control mechanism. Accordingly, focus adjustment can be a particularly difficult and frustrating task, with a poor focus setting typically reducing further the viewer's ability to read and write in a normal manner. Alternately, to obtain a satisfactory focus setting, assistance from a person having normal vision capacity is often required.
Automated focus setting arrangements have been proposed in the prior art for use with various types of camera equipment. Such automated arrangements have typically required the camera to transmit a signal, such as an infrared or sonic signal or the like, for reflection from the image back to the camera, with the camera including appropriate detector means for sensing the reflected signal and responding thereto to adjust a camera lens to a desired setting. However, such automatic focus arrangements have generally required a minimum focus setting length of at least a few feet to obtain satisfactory operation in a relatively economical system. Conversely, such arrangements have not been practical for use in short range focus systems, such as a closed circuit television system for partially sighted persons wherein the focus range of such systems is typically on the order of about one foot and less.
There exists, therefore, a significant need for improvements in closed circuit television systems for use by persons with impaired vision, particularly with respect to providing relatively economical yet accurate automatic focus control. The present invention fulfills these needs and provides further related advantages.